We are investigating and further characterizing the RNA metabolism of cells infected with RNA tumor viruses. Most of the experiments involve mouse cells infected with murine leukemia virus (MuLV), and in some cases other cells and other RNA tumor viruses will be used. Virus-specific RNA in these experiments is detected by RNA-DNA hybridization of cellular RNA with virus-specific DNA synthesized by the "endogenous" reverse transcriptase reaction in MuLV. Three topics are being studied: (1) Virus-specific RNAs from non-producer mouse cells and cells with partial virus expression are being identified and characterized by annealing cellular RNA with 3H DNA probe prepared from endogenous C-type viruses. (2) Labeling kinetics of virus-specific RNA in MuLV infected cells are being studied and characterization of rapidly-labeled virus-specific RNAs is being performed. These RNAs are identified by hybridization to excess virus-specific DNA attached to nitro-cellulose filters. (3) The virus-specific mRNAs are being examined for the presence of "spliced" sequences by S1 nuclease mapping and electron microscopic heteroduplex analysis.